Fuel Pump Problems !

[dpc-gti]

Hi, can anybody please help !

I own a 1983 gti cab.
When I turn the ignition on the fuel relay pulls in and runs for a couple of seconds and then stops.when trying to start the engine it doesnt want to know. If I remove the relay & bridge the terminals so the pump runs continously the engine fires straight into life. Is there a pressure switch that stops the pump when up to pressure. Any ideas what to do greatly appreciated

[richandhazel]

I stand to be corrected here but I'm not aware of any pressure switch. Once the fuel reaches pressure any excess bypasses and returns to the tank. Its quite normal for the pump to run for a few seconds and then stop, I think its done on a timer within the relay and is done to prepressurize the fuel system prior to starting. It doesn't need much as there is an accumulator in the system to hold most of the pressure there.
While you attempt to crank the car over, the pump should run, when you stop cranking (assuming it hasn't started) you should hear the buzzing of the pump for a second or two? If not, I'd say your relay is faulty, common failure, its probably 'sticking' after the doing the initial bit. Another thing you can do is stick a volt meter on the pump terminals and see if you're getting 12 to 13 volts there whilst cranking (as you can't hear the damn thing whilst you're cranking it over). HTH

[dpc-gti]

Thanks for a prompt response.
I forgot to mention I had already replaced the relay as the existing didnt pull in at all.
Put a voltmeter across the supply to the relay first and when cranking went down to approx 6.5 volts. The battery seems to be holding a charge but must admit doesnt spin the engine with much guts. Do you think its past its life? Any other thoughts !!

[richandhazel]

Your battery voltage is dropping to 6.5 volts when you're cranking  
I'd say that is too low. I would expect it to drop maybe to 9 or 10 volts as the starter draws a heavy load, but 6.5 volts , I think thats too much, maybe its dropping too low for the fuel pump to run. Try jump starting it, see if that works.

[66split]

I had the same problem ,i thought my battery was going down and replaced it along with all the big cables, turned out the starter motor was at fault and was draining the battery sharpish.

if your battery is ok(ATS drop test for free) i'd look at the starter next cos if your battery voltage is dropping to 6V the relay stands no chance of holding on. Operating range for "hold on" on a 12v relay is approx9-13v
c ya
66split